The present invention relates to a structure and a composition for an electroluminescent element which can be used in a lap-top computer, television, mobile communications display, or the like, for example.
Electroluminescent elements which make use of the electroluminescence of an organic compound have features such as high visibility due to their self-luminescence, excellent shock resistance properties due to their complete solid state structure, and low drive voltage requirements, etc., and therefore they have received attention for use as luminescent elements in display devices of various types. In order to broaden the use of the aforementioned organic EL (electroluminescent) elements, it is evident that multicolour display capacity is required, as seen in cathode ray tubes (CRT), liquid crystal displays (LCD), and the like.
Conventionally known methods for fabricating a multicolour display device using EL elements include, for example: (1) a method whereby EL materials which emit light in the three primary colours of red (R), green (G) and blue (B) are arranged in a matrix configuration (Japanese Patent Laid-open No. 1577487/1982, Japanese Patent Laid-open No. 147989/1983, Japanese Patent Laid-open No. 214593/1991, and the like); (2) a method whereby the three primary colours, R, G, B, are extracted by combining colour filters with an EL element emitting white light (Japanese Patent Laid-open No. 315988/1989, Japanese Patent Laid-open No. 273496/1990, Japanese Patent Laid-open No. 194895/1991, and the like); (3) a method whereby an EL element emitting red light and a fluorescence converting film are used to convert to the three primary colours, R, G, B (Japanese Patent Laid-open No. 3-152897). However, the methods (2) and (3) described above both have a similar structure to the colour filter used in a colour liquid crystal display device, and consequently they require approximately the same level of expenditure. Moreover, in the method described in (1) above, three different types of luminescence material must be arranged in a very fine matrix configuration.
Therefore, as disclosed in Japanese Patent Laid-open No. 227276/1996, in the method in (1), the luminescent materials for the respective colours are formed over a physical mask in order to fabricate the light-emitting layers for the different colours. Moreover, in U.S. Pat. No. 5,294,869, high walls and low walls are provided between pixels, light-emitting layers are fabricated separately for each colour according to the height of the walls and the vapour deposition angle of electroluminescent material, and furthermore, electrodes are formed by patterning using the aforementioned walls.
However, in methods using a physical mask, not only does the positional registration of the physical mask involve enormous work, but also it is technologically difficult to fabricate a suitable physical mask when manufacturing panels of very high definition, and even supposing that such a mask can be fabricated, it is difficult to carry out accurate patterning of the light-emitting layers. Therefore, it is not practicable to manufacture a high-definition colour panel using physical masks. Moreover, in methods which involve creating walls between pixels, it is necessary to build in the high walls and low walls, and furthermore, a plurality of light-emitting layers must be formed by a plurality of vapour deposition operations whilst varying the vapour deposition angle in the vacuum system.
The present invention overcomes these problems associated with the prior art. A first object of the present invention is to provide an inexpensive electroluminescent element having a novel composition enabling colour display, by providing banks capable of separating light-emitting layers in a passive-drive electroluminescent element.
A second object of the present invention is to provide a manufacture method whereby an electroluminescent element having a novel composition enabling colour display can be manufactured inexpensively, by comprising steps of forming banks in a passive-drive electroluminescent element and introducing light-emitting material therebetween.
The invention achieving the first object is an electroluminescent element provided with layers of electroluminescent material interposed between anodes and cathodes, characterized in that it comprises: an anode group formed by parallel arrangement of a plurality of anodes; a bank group formed by parallel arrangement of banks intersecting with the anode group and having a height which prevents outflow of the electroluminescent material introduced during manufacture; electroluminescent material layers formed inbetween the banks; and a cathode group wherein cathodes running in the longitudinal direction of the electroluminescent material layers are provided on the electroluminescent material layers and are separated electrically for each of the electroluminescent material layers by means of the banks. By adopting a structure which is partitioned by banks, the electroluminescent material layers can be manufactured readily by introducing a liquid of electroluminescent material, and cathode formation can also be carried out in a single operation.
Here, the cathodes are formed in a continuous fashion over a side face of the banks facing in a prescribed direction, the top face of the banks, and the electroluminescent material layers. By adopting this structure, patterning of the cathodes is carried out simultaneously with vapour deposition of the cathodes by making use of the shadow of the banks. Therefore, it is possible to carry out patterning of cathodes formed on organic films which are delicate with respect to processing.
Moreover, the angle formed between at least one side face of the banks and the face on which the banks are installed is an acute angle. By adopting this structure, the cathodes can be formed separately by depositing cathode material from a single direction, and the reliability of patterning can be improved. Moreover, a uniform distance can be maintained between the banks. Thereby, it becomes easier to hit desired pixels when a liquid of electroluminescent material is injected by means of an ink-jet head, for example.
Furthermore, the angle formed between at least one side face of the banks and top face thereof is an acute angle. By adopting this structure, since regions where no cathode material is deposited are generated by the shadow of the banks, the separation of the cathodes is carried out automatically and reliably, and the reliability of patterning can be increased.
Furthermore, the electroluminescent material layers are constituted by light-emitting layers and/or charge transporting layers. The charge transporting layers may be hole injecting and transporting layers or electron injecting and transporting layers. Here, the light-emitting layers emitting light in each of the primary colours for the purpose of providing a colour display are arranged sequentially.
Moreover, in the present invention, each of the anodes constituting the anode group and each of the cathodes constituting the cathode group are connected individually, means being provided for conducting simple matrix driving of the electroluminescent element. By means of this structure, it becomes possible to drive the electroluminescent element by time division, thereby providing an inexpensive, high-capacity, colour electroluminescent element.
The invention for achieving the second object is a method for manufacturing an electroluminescent element provided with layers of electroluminescent material interposed between anodes and cathodes, characterized in that it comprises the steps of: forming an anode group by parallel arrangement of a plurality of anodes on a substrate; forming a bank group by parallel arrangement of banks intersecting with the anode group and having a height which prevents outflow of the electroluminescent material in an electroluminescent material forming step; forming electroluminescent material layers by introducing a liquid of the electroluminescent material inbetween the banks; and forming a cathode group wherein cathodes are electrically separated by means of the banks, by depositing cathode material onto the electroluminescent material layers from a direction which forms a prescribed angle with the longitudinal direction of the banks. By means of these steps, it is possible to form the electroluminescent material layers at normal pressure whilst separating them by means of the banks, without requiring vacuum batch processing involving vapour deposition, or the like.
Moreover, the cathodes can be patterned very finely into thin rectangular shapes for the purpose of simple matrix driving. Here, the banks may be formed such that the angle between the side faces thereof and the face on which the banks are installed is a right angle, the cathode group being formed by depositing cathode material by oblique vapour deposition from a direction confronting the side faces, or a direction perpendicular to the vertical direction of the banks. By this means, cathode patterning is completed simultaneously with cathode vapour deposition, making use of the shadow of the banks. Therefore, it is possible to carry out patterning of cathodes formed on organic films which are delicate with respect to processing.
Moreover, the banks may be formed such that the angle between at least one side face of the banks and the face on which the banks are installed is an acute angle, the cathode group being formed by depositing cathode material by oblique vapour deposition from a direction confronting the one side face or the vertical direction of the banks. Thereby, the reliability of cathode patterning can be increased and the distance between banks can be kept the same as cases where the banks have a rectangular shape, and therefore it becomes easier to hit desired pixels when film material is injected by means of an ink-jet head, or the like.
Moreover, the banks may be formed such that the angle between at least one side face of the banks and the top face thereof is an acute angle, the cathode group being formed by vapour deposition from the vertical direction of the banks. By this means, it is possible to increase the reliability of cathode patterning. Furthermore, non-glare treatment and/or antireflection treatment may be carried out on the surface of the electroluminescent element. By this means, it is possible to improve contrast in the electroluminescent element when used in bright locations.